The present invention relates to micromechanism, particularly to microgrippers for use in catheter-based interventional therapies or remote micro-assembly applications, and more particularly to miniature plastic grippers and fabrication method thereof.
Microactuators for remote and precise manipulation of small objects is great interest in a wide variety of applications. The design and development effort of such microgripper devices would be useful in the art as such will apply to general microfabrication techniques and establish the infrastructure for microengineering efforts including robotics, microtechnology, precision engineering, defense, energy, and biomedical research, as well as use in medical applications, such as for catheter-based interventional therapies and remote assembly or use of micromechanical systems.
When a portion of a blood vessel weakens, it bulges and forms a aneurysm, which is one of the main reasons for strokes as the vessel finally collapses and opens. These aneurysms have traditionally been treated by surgery, where the surgeon will have to open up the area of repair before attempting to surgically repair the aneurysm by clipping it. However, many aneurysms are at critical locations such as in the brain and are either difficult and risky to operate on or it is simply impossible. For the last 20 years, pioneering doctors have used interventional neuroradiology techniques to aid the treatment of brain aneurysms. Long (1-2 meters) and narrow (i.e. 250 .mu.m to 500 .mu.m) catheters are pushed through the arteries in the groin up to the brain to reach the aneurysm. Existing catheter-based interventional instruments rely on simplistic and usually singular means of actuation. These techniques, including balloon angioplasty, are well-established for large vessel treatments such as in the heart. It is crucial that in order to extend this medical practice into the smaller vessels such as those in the brain, the catheter-based tools must be miniaturized. In the most recent method, platinum coils were selected to fill up the aneurysms due to their ability to fill up irregular shapes and their resistance to electrolysis in the vessels when charged. The coils are either pushed through the catheter to the aneurysm by a guide wire or released by the electrolytic dissolution of a solder joint between the guide wire of the catheter and the therapeutic device, which for neurological treatments are approximately 250 .mu.m or less in diameter. Although the charging of the coil causes electrothrombosis around the coil, the time required to release the coil is long (4 mins. to 1 hr.) and many coils are usually needed to fill up a regular sized aneurysm. The extent to which the dissolved material affects the body is unknown and electrolysis requires long terms of current in the brain and sometimes is simply unreliable. These difficulties present potential life-threatening problems to the patient for the surgeon and clinician.
Thus, there has been a need for a micromechanism which can fit into a 250 .mu.m diameter area and which would enable the physician to release and retrieve the coils or other therapeutic device if released at the wrong time or location. A recent approach to satisfying this need involves microgrippers fabricated using known silicon-based techniques or precision micromachining, or a combination of these techniques, with the microgrippers being actuated, for example, by shape-memory alloy (SMA) films or wires deposited on or connected to the jaws of the microgrippers. Such approach is described and claimed in copending U.S. Application Ser. No. 08/446,146, filed May 22, 1995, entitled "Microfabricated Therapeutic Actuator Mechanisms", and assigned to the same assignee.
The present invention also satisfies this need by providing a simply constructed release mechanism formed from a plastic tube, actuated by a microballoon, and which can fit into blood vessels, as well as for other applications involving gripping, sorting and positioning of micron size particles, medicines, etc. While the invention has application in various areas requiring a remotely actuated microgripper, it has particular application in catheter-based interventional therapies. The plastic gripper is made of heat-shrinkable or heat-expandable plastic tubing and is formed around a removable mandrel.